Almost all wheels which run on the ground or the floor comprise a tire part which is made of rubber or metal, this tire part constituting the outer peripheral portion of the wheel, a rim part for supporting the tire part, and a disk or spoke which connects the rim part to the hub.
Since the wheel as stated above is rotated about a wheel axle or shaft, the running direction thereof is limited to a direction perpendicular to the wheel shaft.
For this reason, in the case where the running direction of the wheel is required to be changed, a method is adopted comprising swinging the wheel shaft itself to a direction perpendicular to the running direction by using a steering gear connected to the wheel shaft.
However, it is often difficult to carry out the swinging operation of the wheel using the method comprising swinging the entire wheel in the running direction together with the wheel shaft because of the greater contact frictional force between the tire and the ground (the floor) during stoppage of the wheel. Furthermore, the wheel is required to uselessly follow a locus of a circular arc until it is directed to a desired running direction, which makes change in the running direction of the wheel within a narrow space difficult.
As a means for solving such a problem, a caster device is used which serves to swing the entire wheel about a shaft orientated perpendicular to the wheel shaft and provided at an eccentric position. However, the caster device cannot perfectly solve the above-mentioned problem, and still includes problems such as difficulty in changing the running direction of the wheel during stoppage thereof or difficulty in conversion of the direction of the wheel to that perpendicular to the running direction. In addition, since the caster device easily changes the direction of the wheel shaft during the running thereof, there is a restriction in its use which makes it impossible to increase the running speed of the wheel and the diameter thereof.
Furthermore, a further means to solve the above-mentioned problems has been developed and comprises a wheel device in which two independent wheels with wheel shafts perpendicularly intersecting each other are combined. However, this wheel device has a disadvantage in that it is necessary to provide a means for shifting and drawing in one of the wheels when the other is being used, which results in a complicated construction and a larger-sized device.